Communication system



July 2, 1940; A. R. BoNoRDl-:N 205,659

COMMUNICATION SYSTEM Filed Jan. 1o, 19:59 2 sheets-sheet 1 cAlu/va Alva Msn/Enma ONLY /A/l/ENTO? By A. R. BONORDE N A TTOR/VE y TELEGR. 557' A. R. BONORDEN COMMUNICATION SYSTEM July 2, 1940.

Filed Jan. 10, 1939 2 Sheets-Sheet 2 N ...gk

/Nl/ENTOR m w B R A VI LM R Mm M T A Dwi .mn

' cnice.

. method or operation, greater use isbeing made attendants telegraph set arranged to furnish l visory features in the cord circuits themselves `The invention resides in the intra-cnice trunk "is combined in one lamp a busy indication, a call nated at either end" and the DIOCedule iS Subjack engaged .in an established connection to attendant inserts .plug HlJinto, say, calling 55 Patenteditlyz, 194e 'i i, f 2,206,659

UNITED STATES PATENT ceri COMMUNICATION SYSTEM Allen R. Bonorden, Plainfield, N. J., assignor to Bell `Telephone Laboratories, Incorporated, New York, N. Y.,` a corporation of New York `Application January 10, 1939, Serial No. 250,12 e claims. (o1. rvs-2) This invention relates to telephone `and teleindicate that `an attendant at the opposite end graph systems and more particularly to superof the established connection is` recalling, and `vising and maintaining private wire and switch- (.4) a rapidly flashing lamp at a jack engaged in ing service over` intra-cnice trunks between test the. established connection to indicate that the board positions at the same or at diierent boards attendant `at the opposite end of the established 5 and between test board positions andrepeater connectionhas disconnected.

aisles all of which are in the same telephone or i A better understanding `of `the scope and purtelegraph office. pose of the invention can be obtained from. .the An object of the invention is to simplify signal. following description taken in connection with ing and supervisory facilities in telephone and the attached drawings. in which: telegraph systems wherein an attendant at a Fig. 1 shows `a schematic arrangement of an switchboardmay be connected with any one of a intra-cnice trunk equipped at eachend with one plurality of attendants at the same or at an or more calling only appearances. and a proother switchboard or `at repeater aisles in one Vision for a plurality of combined calling and i answering appearances. Also shown at the left `Another object is to use signaling lamps in an of the trunk in schematic arrangement is .an intra-cnice trunk whereby each lamp` may be attendants telegraph set, and shown atthe right arranged to give a busy indicationpa call indicaof the trunk and in `engageable relation `theretion, recall and disconnect supervisionas desired. with are lalternative connecting means compris` With the adaptation ofthe test board answering ing a patching cord arrangement and `another of intra-cnice communication `facilities both of local battery. v the telephone and .telegraph type, between posi- 1 Fig. 2 shows in schematic arrangement a` ter-v` tions at the same and at different test boards minatng differential duDleX repeater in an nteland between the test boards andthe repeater Office trunkA arranged for engagement, by means aisles. Due to the fact. that communication of a patching cord, with 'the intra-cnice trunk, cords and patching cords in test boards are of said nteroiiice trunk extending to a distant the two-conductor type, the provision of supercnice.

become complicated and expensive` It ishighly shown in Fig. 1 wherein thebusy indication and 30 desirable therefore that there be incorporated in Supervision are Obtained 0n `a Single lamp DIO- such intra-oince trunks. a visual busy indication vided at each appearance of .the trunk. at :a and supervisory signals in `order to obtain the` switchboard or test board position,` or at the redesired operating efficiency.` `peater aisle. A` detailed description of the opera- `According to the present invention the com" tion of an intro-once trunk circuit such as shown 35 plicated and expensive cord circuits are elimin Fig. 1 of the drawings will now be given. The inated by incorporating `the busy, signaling and invention will be described for telegraph operasupervisory features in the trunk circuit without tion. it beine understood .that a telephone Set may increasing the space required in the jack neld be readily substituted. for the'` telegraph set by of the switchboard and the test board. anyone skilled 'in the art. c 40 A feature of theinvention is the incorporation First the lnVentiOnWll be CeSCIilOedv by estabe i in each intramm trunk `0f a, visualbusy indi.. lishing a connection betweena test board posication and supervisory signal, whereby economy tion at the A end "0f ther intra-Cinca trunk and the desired operating eiiiciency are obtained. ShOWn in Fig-` 1 .andi a test beard `pOSilJin and/01 Another feature is the provision whereby vthere .aisle stations `atthelfB end. ."Calls may be crgindication, recall and disconnection supervision. .Stanllaily the Same f01^"b0th ends, except that Still another feature is that `the various sig- Jthe A end may and usually does include means 119,15 Combined'in onelamp may beyarranged to forextending calls` toandfrom int'eroiice trunks `produce (l) a steadily `lighted lamp at an idle OieSi' boards 'in Oiinel` Cities. l 50 trunk jack to indicate abusy condition forthe i l trunk, (2) a rapidly flashing lamp at an idle i I Omgmatmg a' Gail .from the' A en@ trunk jack to indicate an incoming call, (3) `in- Assume `that for the sake of illustration thatl termittent periods of hashing ofthe lamp at a the call originatesatthe right', or"A, end. The

only jack ||2, opens switch ||3 and operates key ||4 for connecting local battery to the attendants telegraph set. The insertion of plug I I closes a circuit extending from grounded battery ||5, associated spring of jack I|2,v conductors llt and I through the winding of relay II 8 to ground. Relay H8 operates and thereby opens at its outermost right armature and contact a short circuit across the transmission crcuit IST-|59 and closes at its outer left arma-` ture .and outer front contact, a circuit extending from ground, conductor |I9, then in parallel over each of conductors |29, to each of all the combined calling and answering jacks I2| at the originating, or A end; the parallel path ci each jack being completed over. the contact in engagement with the middle spring, in normal position, of a jack such as that designated I2|, through a lamp such as that designated |22, to grounded battery. Lamp |22 at each of the combined calling and answering jacks lights steadily to indicate a busy condition for the trunk circuit shown. Relay H8, in` operating, also connects at its outer left yarmature and inner front contact, a circuit extending from ground, conductors |23, |5|, |24 and |25 to the other calling only jacks, in parallel, such as` that designated |26; the parallel path of each being completed over the contact in engagement with the middle spring, 'in normal position, of a jack', such as that designated |29, through a lamp such as that designated |21, to grounded battery. Lamp |21 lights steadily to indicate a busy condition. `Rel-ay Il, in operating, also closes at its middle right armature and front contact, a circuit extending from grounded battery, outer right armature and inner back contact of relay |49, conductor |28, front contact and right middle armature of relay ||8, conducf tor |29, resistance L, through the winding of auxiliary signal relay |39 to ground. Relay |39 operates and thereby closes at its left armatures and contacts, circuits for respectively operating pilot lamp" |3| and buzzer |32 at the repeater .aisles or other convenient points near the called end of the trunk, in order to attract yattention should the called position vbe unattended. The resistance of the auxiliary signal relay suchfas that designated |39, is small, being of the order of one ohm, and for that reason, because it is connected in multiple to all interoflice trunks yterminating in one position, there is included in the circuitl comprising a conductor such as that designated |29, a resistance L which has a value of about 240 ohms, or that equivalent to that of. a lamp. Relay ||8, in operating, also closes at its make-before-break, Contact in engageable relation with its inner left armature, a circuit extending from the grounded interrupter |33, .conductor |34, makegbefore-break contacts of relay H9, conductors |49, |35, |36 andv |31, contact in engagement with the middle spring, in normal position, of the calling and answering jack |38, through lamp |39 to grounded battery.

The circuit just traced' also extends over conductor |52 to parallel paths extending similarlyy to other lamps such as that designated |39 at the other calling and answering jacks (not shown) at the B end. Lamps, such as that designated |39, give, at this time a rapidlyflashing signal indieating that an incoming call iswaiting on calling and answering jacks at the B end. Lamp |43 at jack ||2 whereat the call originated lights 'steadily in a circuit extending from ground at the inner back contact and. outer left armature ofl relay |49, conductors |4| and |42, contact in engagement with the middle spring inoperated position of jack H2, through lamp |43 to grounded battery. Lamp |43 will operate steadily to indicate that the called attendant has not yet answered.

Answering the Call sition as shown. The insertion of plug |44 closes a` circuit extending from grounded battery asvsociated with `jack |33, conductors |39 and |41,

,. through the winding of relay |48 to ground. Re-

lay |4| operates and thereby Opens at its outermost left yarmature and contact the other short circuit across the transmission path HiT-|58, and closes at its outer right armature and outer iront contact a circuit extending from ground over conductor |49 and then over conductors |35, |35 and |42, as hereinbefore traced, to` change the rapid flashing of`all of the other combined calling and answering-lamps, or appearances, at the B end to ysteady lights to indicate at `such appearances that the trunk circuit is busy. Relay illt, in operating, also closes at its outer right armature and inner front contact a circuit extending irom ground,conductor |59, then over conductor |24'as hereinbefore traced to add another groundvfor maintaining steadily klighted lamps at'all the calling only appearances at both the fA and B ends. Up to this time lamp |43 associated with the calling only jack H2 rat which the lcall originated is maintainedI steadily lighted in a vcircuit extending over conductors |42 and |4| to ground at the outermost left armature and back contact of relay |49] Rethrough the right, or secondary, winding of the.

relay, conductor |53 to the junction of conductors |59 and` |23; which are grounded respectively, at 'the inner iront contact of the outer right armature of relay. |48 and at the inner front contact of the outer left armature of relay H8 as previouslydescribed. Relayl |49, in'operating, opens at its outer right armature and contact, the oircuit hereinbefore traced for operating the auxiliarysignal relay |34. also disconnects ground at its outer'leftarmature and inner back contact, from the two circuits respectively extending over conductors |54 and '|4l to lextingfuishlamps |39 and |43, respectively associated with jacks |38 and ||2 which are engagedin the established connection. Relay lili?, in operating, supplements ground at its outerv front contact and inner left armature to maintain a steady light at lamps such as' |22 at all the calling and answering appearances of the trunk at end Aand connects ground at contacts |55 to conductors |56 and |35 to supplement answering appearancesof the trunk at end B Relay |40, in operating,

in a steadily lighted condition. Therefore, for normal operation, all lamps are lighted steadily as busy indication,vexcept th'se lamps associated with the jacks where the calling and answering cords at the A and "B ends respectively, are connected. The last-mentioned lamps Aare extinguished, the extinguishing of the lamp at the calling end A indicates that the called party at end B has answered.

The trunk` is now arranged for communication in either direction over the transmission trunk conductors |51 and |58. The trunk, as stated hereinbefore, is adaptable for either telephone or telegraph transmission. In the case of telegraph transmission as herein described in detail, transmission conductors |51 and |58 are short-circuited at the outermost right armature and contact of either relay ||8 or |48, depending on the end oi the trunk at which the call originates, until the called party answers thus holding the calling telegraph line in a marking, or closed condition.

Disconnectz'ng at the culled` end after communication,

Assuming that the attendant at the called, or B end of the trunk circuit disconnects by removing plug HM from jack 38, relay |48 releases thereby replacing at its outermost left armature and contact the short circuit across the transmissionconductors` |51 and |58 to hold 4the calling line ina marking or closed, condition. Relay |48, in releasing, opens at its innermost left armature and contact the operating circuit for relay 4Q which circuit extends through the left, or primary, winding of the latter relay. i

ily in a circuit traceable from grounded battery,

lamp l39, the middle spring, in normal position, engaged with its lower contact, conductors |31, |36 and |5, closed contacts |55 to ground at relay M0. The attendant at end A upon observing the rapid flashing of lamp |43 atthis time removes plug lfrom jack l2 and thereby` causes the release oi relay H8. Relay IIB, in releasing, supplements at its outermost rightarmature and contact the short circuit across transmission trunk conductors |51 and |58 and at its outer left armature and inner front contact disconnects ground from the circuit extending over conductors |23, |5I and |24 to the parallel paths, such `as that designated |25, the

middle spring, in normal position, engaged to the lower Contact of the jack, such as that designated |26 through lamp |21 to grounded battery.

The lamps such` as that designated |21 become extinguished. -Relay H8, in releasing, also opens the locking circuit for relay |40 which now releases. Y

Relay |40, inireleasing, removes at its contact |55 the ground connection from the circuit extending over conductors |56 and |36, then over parallel paths such as those designated |31and |52 respectively, the middle springs in normal position,` engaged to their respective lower contacts, through the lamps such as that designated |39 to grounded battery. Likewise atthe inner left armature but at the outer front contact of relay |40, the circuit for effecting a steady light on the calling and answering appearance lamps atthe A end is opened and lamps such as lamp |22 become extinguished. Relay |40, in releasing, also closed at its outer left armature and back contact, parallel circuits for short-circuiting the interrupters |33 and I59`and the trunk is now restored to normal. i

Disconnecting at the` calling end after commui nication.

Assuming that the attendant at the calling, or A", end of the trunk circuit disconnects first by removing plug I `from jack H2, relay ||8 releases instead of relay |48 which released prior to relay ||8 when the disconnection was effected first at the called or B end. Afurther description is not deemedl necessary in View of the description hereinbefore given for a disconnection at the called, 0r B, end.

. Originating a caZZ from the B end Assume that the call originates at the left, or B end. Having in mind the description of the -establishment of a call originating at the A end, it is lbelieved that a brief description only of the establishment of a call originating at the` B" end will be sufficient. The attendant inserts a plug m4 into a jack such as that designated |25 or 38, to close an operating circuit for relay` |48. Relay |48 operates and thereby closes `a circuit at its outer right armature and outer front contact,` conductor |49 to produce a steady light on the lamps at all `the calling and answering appearances,. except the one into which plug I4@ is inserted, assuming that one of the calling and answering jacks is selected. Also at the same armature, but in engagement with the associated inner front contact, relay |48 closes a circuit including conductors |50, |24 and |25 to produce a steady Alight on the lamps associated'with the calling only appearances at both ends except the one into which plug |44 is inserted assuming that the connection be originated at one of the calling only appearances. 'Ihe ciri cuit normally closed at the outer back contact V and outer left armature of the relay furnishes ground over conductor |54 to light the lamp associated with the jack at which the call originated.

Relay |48, inoperating, ycloses at its makebefore-break contact at its inner right armature, a `circuit extending from grounded interrupter |59 and over conductor H9 to cause a` rapid dashing of the lamps at all the calling and answering appearances at the A endand at its middle left armature and contact closes an obvious `path for operating the auxiliary signal relay which in turn controls the audible signal and pilot lamp at the called end. An attendant at any one of the calling and` answering positions at the "A end, upon observing the flashing of the lamps, inserts plug into a jack associated `with a flashing lamp to close a circuit over conductor I|1 to operate relay H8. The insertion of plug rst transfersthe middle spring of the jack into which the plug is inserted from a lower to an upper contact and thereby changes the associated lamp from the` Relay H8, in operating, short-circuits at its outer left armature yand outer front contact, interrupter tot, changes the lamps at all the other "calling and answering appearances from a flashing to a steady light condition and at its outer left armaturev and inner front contact closes a circuit for producing a steady light on the lamps in all the calling only appearances at both the "A and "B ends, it being kept in mind that should jacks at one of the calling only" appearances lat the B end be selected for originating a call, its associated lamp will produce a steady light by means of the circuit extending to ground at contact l. l

Relay itil in operating, completes the same circuits as hereinbeiore described in connection with a call originating at the A end. Likewise a disconnect and a recall signal may be had as hereinbeiore described.

Originating a call to an outside Zine including a repeater Assume that akcall originates at the "B end for termination at an oiiice in another city. The call is first established to the "A end in the manner as hereinbelore described for a call originating at the "B end. The attendant at the "A" end upon receiving the request from the attendant at the "B" end removes plug lil from jack iZl and inserts plug itt into jack; 2H of the interofce trunk circuit. He then inserts plug ltlinto jack l2l after waiting approximately two seconds. The interoflice trunk circuit is normally closed at Contact` 2 l the circuit extending from grounded positive battery 2l?, through the right-hand winding of biased relay 2I3, conductor Zlil, contact 2th, conductor 2id, through the upper windings, in series, of send relay 2H and differentially connected relay Zit, armature and normally engaged contact of receiving relay 2I9 to grounded negative battery. Current flows through the left-hand winding of relay 253 in one direction and in parallel through the righthand winding in the opposite direction so that relay 2l@ normally is iny a released position, the current through the left-hand winding being continuous to effect a bias condition. Relay 243 is shown in Fig. 2 of the drawings, as being in a released position.

The insertion of plug lfl into jack 2l l Vopens contacts ili to send an open. signal of comparatively long duration through the upper windings in series-of relays 2li and 258.l The bias current normally flowing from the grounded negative source at the contact normally engaged to the armature oi'relay 259 through the lower windings, in series, oi relays 2l8 and 2H, artificial line 235i to ground now causes relays 2 i8 and 2H to operate to their released positions. Relay 2li, in operating to its released position, closes a circuit extending from its negatively poled Contact and armature, conductor 22d, then over parallel paths one extending through the right-hand `winding of relay 'Mil to the trunk conductor 22l, and the other through the left-hand winding, artificial line 222 to ground. Relay Zit, being of a type having a diierentialcharacteristic, does not operate in response to the current from the grounded battery sources that are in engageable relation with the armature of relay Ril.

At the opposite end or" the trunk circuit 22E, not shown, is kan arrange-:n1 Lt, to that shown in Fig. 2 of the drawings, as constituting the interofce trunk terminal equipment corresponding to receiving relay 2id, differentially connected relay 2l`8, send relay 2H, jack 2li, relay 213, and the signaling equipment controlled thereby. The equipment parts at the opposite end will hereinafter be referred to by reference characters similar to those designating their respectively corresponding. parts at the local end, except that to such corresponding characters will be added prime marks. It will be assumed therefore, for the sake of illustration, that the current that was stated hereinabove as flowing from the negatively poled contacts of relay 2H is being received by a receiving relay 2li-l'. Relay 2l9 operates and thereby disconnects its armature from its negatively poled contact and closes a circuit extending from the grounded positive battery 2i2', through the right-hand winding of relay 2&3', conductor 2id', contacts 2lb', conductor 2l6', through the upper windings, in series, of relays 2H' and 2id', armature and contacts normally disengaged from the armature of relay .2!9', armature and positively poled contact of relay Zl. Since'the. opposite ends of the circuit just traced are now positively poled, relay M3 operates under the iniluence of the continuous current in its left-hand winding. Relay 2l3, in operating, closes at its armature 'and contact, a circuit extending from ground at jack contacts 233', conductor 22d', armature and contact of relay 2id', through the winding of slow-to-release relay 225', upper armature and back contact of relay 226', to grounded negative battery 22T. Relay 225 operates to thereby close at its armature and contact, a path through the winding of relay 226' to grounded negative battery. Relay 225 is of the slow-to-operate type to guard against lany short open periods in the line circuit just as those used for communication purposes. As hereinbefore stated an open period for calling purposes is comparatively long and is oi suihcient duration to cause relay 226' to operate. Also relay 225 being of the slow-to-release type does not release in response to the open period ordinarily employed for the inessageimpulses. Relay 226', inI operating, closes at its upper armature and front contact, a circuit extending from grounded negative battery through the winding of relay 226', armature and contact of relay 225', through the winding of relay 22d', upper armature and iront contact oi relay 226', conductor 223', through lamp 229', conductor 239', through the winding of pilot relay itil' to ground. Lamp 229' does not light nor will relay 225 hold in this circuit. Relay 226', in operating, also prepares at its lower armature and contact a path for operating relay 232'. When relay 225' eventually releases, relay 232' will -operate provided relay 2l3 is still in the operated position. Relay 232 locks to ground at jack contact 233 .and causes lamp 229' to light to indicate to the attendant at the distant office that a call is being made. The above operations occur during the interval elapsing between the insertion oi plug |764 in jack 2li and plug 68 in` jack l2 l.

When the attendant at the local oihce ccmpletes the patch, the right-hand Winding of relay 2i3 again becomes energized and the relay having the characteristic of a differential type again releases and thereby opens at its armature and Contact the operating circuit for relays 225' and 226' which release. Lamp 229' remains lighted until the attendant at the distant oilce inserts plug lll' into jack 2H at which.

inserting the plug.

Relay 232' releases and removes grounded battery from. the operating circuit for lamp 229. Lamp 229 is extinguished. The interoice trunk is now in condition for communication between the B attendant in the local oflice and the attendant in the distant office.

Recall` signal A recallsignal may be initiated by the attendant at either end after the other attendant has answered. This is accomplished by momentarily disconnecting the plug from the jack and by re- These operations are-repeated slowly to reproduce intermittent periods of iiashing of the lamp at the opposite end each time the plug is removed as described for a disconnect. The attendant at `the opposite end upon observing the short periods of rapidflash` ing of the lamp associated'withthe jack to which the plug is connected will challenge with his set if connected or will replace the patch cord |58 with the plug attached to his set in the jack associated with the iiashing lamp and the connection is thereby reestablished.

Originating a call at the distant end to the attendant at the A end When an incoming call is received over line 22| to operate receiving relay 2| 9 at the local ofce, the armature of relay 2|!) engages its positively poled contact and thereby closes a circuit extending from grounded positive battery 2|2, through the right-hand winding of relay 21S, conductor 2M, vcontact 2| 5, conductor 2|6, through the upper windings, in series, of relays 2H and 2|8, armature and normally disengaged contact of relay 2| 9, armature and positively poled contact of relay 2|8. `Inasmuch as both ends of the circuit, just traced are positively poled, relay 2|3 operatesunder the influence of the current flowing through its left-hand winding. Relay 2|3, in operating, closes at its armature and contact, a` circuit extending from grounded battery 221, armature and back contact ofirelay 226, through the winding of relay 225, contact and armature of relay 2|3,` conductor 224, to ground at contact 233. Relay 225 operates to close a circuit extending from grounded conductor 224, armature and contact of relay 2|3, armature and contact of relay 225, through the Winding of relay 22|;` to grounded battery. Relay 226 being of the slow-to-operate type operates slowly to open at its upper armature and front contact, the operating circuit of relay 225. Relay 225 also prepares at its lower front contact a path which includes the winding of relay 232. i

Relay 225 after a short interval releases and completes at its make-before-break contact 23| the circuit previously prepared, which extends from grounded conductor 224, armature and contact of relay 2|3, contacts 23|, contacts and lower armature of relay 226, through the winding of relay 232 to grounded battery. Relay 232 operates to close a locking circuit for itself extending from grounded battery through its winding and lower contact and lower armature` to grounded conductor 224. At its upper armature and contact relay 232, in operating, closes a circuit for lighting lamp 229 and operating the auxiliary relay `at the B and over lead 23D. The release of relay 225 releases relay 226.

The attendant at the A end observing the lighting of lamp 229 inserts plug into jack 2| I `and communicates `with the calling attendant at the distant oicef The insertion ofthe plug intojack 2| opens contact 2| 5 and the ground connection `233. Relay 232, upon having its locking circuitopened at contact 233 releases and at its upper armature and contact, removes grounded battery from the lighted circuit of lamp 229. Lamp 229 is thereby extinguished.

The attendant at the A end in response to the request of the distant calling attendant may complete the call over an intra-office trunk to the `desired point in the oice. The attendant at the A end inserts plug |68 into a jack, say jack |2| of the desired intra-,office trunk such as shown in Hg. 1, removes plug from jack 2|| and connects theother end of the patch cord |63 to the interoflice trunk by inserting plug |64 into jack 2| l When the attendant at the B end answers the call signal as hereinbefore described,

ne will be connected for communication purposes with the attendantat the distant oiiice over the intra-oice trunk shown in Fig. 1 and the interoflice trunk which interconnect the A end and the cnice in the distant city.

The release of the connection established between a telegraph set at the Bi end and a telegraph. set at the ofiiceof the `distant city must be originated at the B en'd and the attendant at the A end upon observing the disconnect signal, at say lamp |22, will remove patching cord |63 from the jack from which itis engaged.

` Rsum In accordance with the above it will be noted that the following signaling and supervisory conditions are among those afforded on a single signal lamp associated with an intra-oline trunk: dark lampno plug inserted at associated jacktrunk is idle; hashing lampf-no plug inserted at associated jack-calling;

jacke-'called party answered; steadily light lamp-no plug inserted at associated jacktrunk is busy; ashing lamp-,plug inserted at associated jack-disconnectg and intermittent periods of flashing lamp-plug inserted at associated jack-recall.

What is claimed is:

1. A switching system for communication purposes comprising a plurality of connecting terminals, a circuit interconnecting said terminals, signals for said circuit respectively mounted in receiving sets respectively comprising plugs arranged for connection to said terminals, and

means included in said circuit and controlled by each of said plugs `for transmitting current for effecting at each of said signals a plurality of diiierent signaling and supervisory indications of no current, steady current, rapidly pulsating current and intermittent flashing current owing in said circuit. i

2. A switching system for communication purposes according to Claim l wherein said means comprises a source of steady current, aninter- `rupter device connected with said source, and a steadily lighted lamp extinguishedplug inserted at associated proximity to said terminals, transmitting and poses according to Claim 1 wherein saidlconnecting terminals are spring jacks for respectively terminating opposite ends of said circuit, said signals are lamps respectively associated With said spring jacks, and said means comprises a current source, a plurality oi interrupting devices and a relay arrangement for connecting, as desired, said current'source and said interrupting devices to each of said signals. i

5. In a manually operated switching system, a plurality of switchboards, a plurality of aisle stations, trunk circuits interconnecting said switchboards and for connecting said switchboards Withsaid aisle stations, connecting elements for each end of said trunk circuits at each of said switchboards, linlrf-circuits for interconnecting any two of said connecting elements at a switch-` board, a signal associated with each ci said connecting elements and said aisle stations, and means in each of said trunk circuits for giving, as desired, in each of said signals a lousy indication, a call indication and recali anddisconneet supervision.

6. 1n a manually operated switching system, a

plurality of svvitchlfioardes,l trunk circuits interconnecting said switchboards, connecting elements terminating each of said trunk circuits at each of said switchboards, other circuits terminating in each of said switoiiboards, other connecting elementsy terminating each of said other circuits at said switchboard, link circuits for interconnecting any one of said trunk circuits and any one of said other circuits at any' one of said switchboards, supervisory signals as sociated with each ci the first-mentioned connesting elements, means in each of said trunk circuits for effecting, when said trunk circuits' are respectively connected through said link circuit to anyone of said other circuits in each of.

said signals associated with an engaged trunk circuit indication of a call initiated, an incoming call, a call answered, a busy condition,a recall and a disconnection as desired, and means for adapting said connecting elements for use as a combined answering and calling appearance or as a calling only appearance. 

